Giant leap for palaeontology
Huge footsteps have put
Zimbabwe on the dinosaur map, writes Theagarten Lingham-Soliar
Thursday March 28, 2002
The Guardian
As the storm clouds gathered over Europe
just before the first world war , Werner Janensch and Edwin Hennig, of the
Natural History Museum of Berlin, had very different things on their mind.
Their search for dinosaurs in Africa had culminated in one of the greatest
palaeontological finds in the world, hundreds of tons of dinosaur skeletons
that thrust Africa into the global forefront of dinosaur research.
The discovery was at Tendaguru, in Tanzania, and included a
variety of dinosaurs. But the real icing on the cake was the complete skeleton
of the then largest known animal to walk on Earth, the 80-tonne plant-eating
sauropod dinosaur Brachiosaurus. Today, it is only exceeded in size by the
140-tonne ultrasaurus, which could just be a fully grown Brachiosaurus.
Brachiosaurus roamed a land of conifer trees and coastal flood
plains more than 100m years ago when Africa was still connected to North
America. Consequently, one might expect that these monster dinosaurs would
have left their footprints on these muddy ancient shores, information that
could be vital in understanding the behaviour of these giants.
Thus, it was particularly disappointing that not a single
footprint of Brachiosaurus was found in Tanzania. Indeed, not a single giant
sauropod footprint had been found in the whole of sub-Saharan Africa. Not
until now, that is. In a paper submitted to the international journal Geology,
a team of researchers from Zimbabwe - Ali Kaci Ahmed and Tim Broderick - and
myself, reported the first sub-Saharan footprints of giant sauropod dinosaurs,
discovered in the Zambezi Valley. One of the footprints, close to a metre long
and 22cm deep, caught in the afternoon sunlight looked so fresh it could have
been made only hours before, and not 150m years ago.
This must rank as one of the best preserved giant dinosaur
footprints anywhere in the world. Previous identification of the bones of
Brachiosaurus no more than 50km away, together with the great size of these
footprints make it extremely likely that they belong to a Brachiosaurid-type
dinosaur weighing 60-70 tonnes.
But what is most remarkable in our footprint is the raised
ridge surrounding the entire impression, exactly like the ridge surrounding a
meteorite crater and clearly to do with considerable impact in both cases. The
preservation of this kind of ridge is rare in even the best preserved
footprints seen in the USA and Australia.
Once the mud laid down hardens, it has to be covered by
another layer of mud to be preserved, and both layers, over millions of years,
are converted into solid rock. For these footprints to see the light of day
again, severe erosion of the top layer by floodwaters and wind must take place
- and it is the ridges around footprints that will be eroded first and
quickest. It has to be caught at the very inception of the erosion process.
This preservation gives a graphic picture of the tremendous forces generated
as each foot of this giant dinosaur impacted with the ground (calculated at
about 27, 000 pounds per square foot).
So great is the force that firm mud from much deeper down is
forced up to the surface around the edges of the foot to create a reasonably
durable ridge. A ridge of sloppier mud would collapse within hours or less.
Although the Tendaguru formation and the famous Morrison formation of the USA
show striking similarity in the presence of the giant sauropod Brachiosaurus,
the most notable difference is the absence of skeletons (or footprints) of
large theropod (carnivorous) dinosaurs at Tendaguru comparable to the Morrison
allosaurus.
Here, Zimbabwe comes into its own. Within a radius of 500m of
the giant sauropod footprints we found more than 100 footprints belonging to a
large theropod calculated at about four metres tall. We also found five
trackways within metres of each other, with compelling implications of group
predatory behaviour. So close were some of these trackways that the tracks of
different dinosaurs overlap while still retaining their individual clarity.
The Zambezi Valley dinosaurs are a huge jump ahead of those of
Tendaguru. Zimbabwe, and southern Africa in general, must rank now as one of
the key dinosaur localities in the world. Ichnology, the study of tracks and
traces, is a fascinating subject. It is also a beguiling subject as Winnie the
Pooh discovered when he and piglet were tracking Woozles (and Wizzles) in the
Hundred Acre Wood.
It was only when Christopher Robin pointed it out that they
realised that they were following their own footprints in circles. Poor Pooh
sadly declared he was "a bear of very little brain." But Pooh would be pleased
to know that ichnology is today a science at the top of dinosaur research,
with much better data than was available to him.
* Professor Theagarten Lingham-Soliar is in the Zoology
Department, University of Durban-Westville. Dr Ali Kaci Ahmed is with the
Zimbabwe Geological Survey and Tim Broderick is director of Jeremy Prince,
Hydrologists, Harare, Zimbabwe.